Final (Second) Exam, Apr. 24, 2001

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200 points total

PART I. 80 points. 20 points each.

Answer 4 of the following 5 questions (1-5):

Each of these answers is restricted to
about 1/2 page.

1.
Although a number of foods (plant) have been accepted as part of our diet for many years, some may be detrimental. Explain this using 3 specific examples.

5.Discuss the flower pigments in terms of their chemical makeup and their natural roles.

PART II. 30 points.

Answer 1 of the following 2 questions (6-7):

Each of these answers is restricted to
about 1/2 page.

6.
Using information from this course, explain in chemical and ecological terms what is going on in the figure. To enlarge this image, click on it, and to return to the original figure with the question, click on the BACK button in your web browser.

7.Explain in chemical terms how the insects in the figure utilize the host plant also shown in the figure. To enlarge this image, click on it, and
to return to the original figure with the question, click on the BACK button in your web browser.

PART III. 40 points. 10 points each.

Each of these answers is restricted to about 4 lines.

8. Briefly, explain the meaning (and if
appropriate, give an example) of any 4 of the following 5 terms:

Flavor is a combination of taste, odor, texture and common chemical sense.

Taste is the perception of higher molecular weight, hydrophilic, nonvolatile compounds usually requiring fairly direct contact with the source. In humans, this takes place in the oral cavity, mainly on the tongue.

Odor is the sensing of lower molecular weight, hydrophobic, volatile compounds usually not requiring direct contact with the source. In humans, this takes place in the nasal cavity.

Texture, the feel of food (e.g., rough, smooth, etc.) is also an important facet of flavor.

The common chemical sense is a sensation, most often perceived in the delicate lining of the oral cavity. Pungency and astringency would be examples.

3. Take one example of a botanical folk medicine and explain its chemical and physiological basis.

As in question #1 above, there are many many possible examples here. Two examples are:

Opium. Opium and opium poppy extracts have been used as analgesics. One of the main active ingredients is morphine, an analog of endorphins (ent-kephalins) which serve to stimulate a pleasure response and suppress pain responses.

Willow extract. Willow teas have been important in pain relief in most cultures across the northern hemisphere. The active ingredient is salicylic acid, which is derived from salicin ( a glycoside), an it inhibits the COX-1 (cyclo-oxygenase) enzyme that converts arachidonic acid to prostagladins. This diminishes inflammation and pain.

Mycotoxins are toxins produced by nonmushroom fungi, and examples would include aflatoxin and possibly even penicillin.

The most probable function is to combat other microorganisms that compete for the same food source, e.g., antibiotic action.

One can also imagine other possible roles such as protecting a food source by deterring animals that might consume the food source or by providing protection for a plant symbiont as some mycorrhizal fungi seem to do.

5. Discuss the flower pigments in terms of their chemical makeup and their natural roles.

This has the potential to be a more complex question than necessary.

The main flower pigments are the carotenoids and flavonoids. In some groups, the betalains are important and occasionally chlorophyll. Flowers usually do not carry on photosynthesis, so the photosynthesis pigments are usually not significant. The flower pigments are hydrophilic (flavonoids and betalains) or hydrophobic (cartenoids), and this influences their subcellular location, i.e., vacuolar or membranes and lipid droplets respectively.

The role of these pigments is to attract animal pollinators, and that can be somewhat selective with certain colors attracting particular groups of pollinators, e.g., red often attracts birds and UV-absorbing pigments are visible mainly to bees. Sometimes, special pigment patterns guide the pollinators, i.e., nectar guides.

7.Explain in chemical terms how the insects in the figure utilize the host plant also shown in the figure.

The insects feed on the milkweed which is toxic to most animals due to cardiac glycosides. These insects have evolved resistance to the cardiac glycosides and are actually able to accumulate them in specific parts of their body (aposomatic). This provides them with some protection and they are brightly colored to warn potential predators. Interestingly, cardiac glycosides accumulated by the monarch butterfly caterpillars are passed along through metamorphosis to the butterfly

8c. Doctrine of signatures This is an ancient philosophy that holds that plants contain a sign or signature which reveals how they can be used by people. For example, walnut resembles a human brain and therefore should provide brain remedies.

8e. Kairomones are chemical signals between different species where the signal mainly benefits the producers. Examples include the insect pheromones released by some flowers, flavonoids released by legume roots to attract the N2-fixing symbiotic bacteria and the semiochemicals released by corn leaves under attack by caterpillars.